In conventional laser video projectors all of the red, green and blue light beam components are transmitted to a horizontal scanner or rotating polygon mirror having a predetermined number of facets and then onto three lenses, preferably 454-640 nm AR coated high power achromats to a frame scanner or scanning mirror. The three lenses positioned between the rotating polygon mirror and the scanning mirror are 55 mm, 25 mm cylindrical and 55 mm to 160 mm, respectively. Such a projector is disclosed in U.S. Pat. No. 5,136,426, which is assigned to the same assignee as the present invention and is incorporated by reference herein for all purposes. The image on the scanning mirror is then directed to a fixed steering mirror to a viewing surface. This viewing surface can be a solid surface, such as a conventional projector screen or wall. Other conventional scanning means could be used with the present invention, such as the scanning means disclosed in U.S. Pat. Nos. 4,613,201; 4,611,245; 4,979,030; or 4,978,202, that are incorporated by reference herein for all purposes.
It is known by those skilled in the art that when an image is moved horizontally by a rotating steering mirror, the image needs to be rotated responsive to this horizontal movement to maintain the image right side up. Conventional rotator means or assemblies to rotate the image responsive to the horizontal movement include a dove prism, K-mirror or pechan prism. However, because of the expanding nature of the image, or, in other words, the diverging image transmitted from the scanning mirror of the projector, a properly sized rotator assembly and the steering mirror are larger than desired and, in turn, require large motors for moving the steering mirror and rotator assembly.
Dove prisms have been used in the past for rotating the image responsive to the horizontal movement. U.S. Pat. Nos. 2,966,096; 3,894,798; 4,235,535; and 4,645,318 are examples of conventional dove prisms that are incorporated by reference herein for all purposes. Another example of a conventional dove prism used to rotate a laser image responsive to horizontal movement is a 2".times.2".times.6.5" dove prism having a prism corner cut of 55.degree. with the index of refraction of the glass stock being n=1.51. This dove prism requires a 5".times.5" steering mirror, weighs approximately 1150 grams (2.5 lbs.) and requires a rotation stage with a central aperture of at least 3".
U.S. Pat. No. 4,235,535 discloses a projector for projecting images onto a cylindrical screen for purposes of simulating the view of a ship in a ship simulator. The image is projected onto the dove prism 13 for rotation responsive to the horizontal movement of the image. The horizontal and vertical movement of the image are controlled by stepping motors. These stepping motors can be operated manually or by computer independently of each other. The speed of rotation of the dove prism 13 is one-half the horizontal movement.
Mirrors have also been used in the past for rotating an image. As best shown in FIG. 1 of U.S. Pat. No. 3,326,077, a lamp 52 is located below a photocell 54 directly behind a condensing lens system 56 which is designed to collimate the light emitted by the lamp onto a slightly inwardly tapered beam which illuminates the bottom slit pattern 50a. (col. 3, lns. 15-20) Also disclosed are mirrors 32, 36 and 60. (col. 4, lns. 7-11) U.S. Pat. No. 3,326,077 is incorporated by reference herein for all purposes.
FIG. 1 of the present invention illustrates a conventional K-mirror assembly. In this K-mirror the scanning mirror M.sub.1 projects a diverging image onto a 1".times.1" mirror M.sub.2 which in turn reflects onto a 2".times.2" mirror M.sub.3 which in turn reflects onto a 4".times.5" mirror M.sub.4 to rotate the image. This K-mirror assembly then transmits the image to the steering mirror M.sub.5 which is sized at 7".times.6" to properly steer the complete image.
A conventional pechan prism to rotate an image is disclosed in U.S. Pat. No. 4,645,318. Conventional prisms, such as the dove and pechan prisms, are generally custom manufactured to specification by optic fabrication shops such as CVI of Albuquerque, N. Mex.; Rocky Mountain Instrument Co. of Longmont, Colo. and Kollmorgen Corporation of Northampton, Mass.
It has also been known in the past to use optics to collimate an image, as disclosed in U.S. Pat. Nos. 4,294,506 and 4,906,061. However, the collimated image has not then been projected through a rotator assembly, such as a K-mirror, pechan prism or dove prism, to rotate the image responsive to the horizontal movement of the steering mirror. Moreover, the angular information of the collimated image has not subsequently been restored after being transmitted through the rotator assembly so that the image continues to diverge.
U.S. Pat. No. 4,294,506 discloses an argon laser 36 where the image is passed through an expander lens 39, comprising a convex lens 39a and a concave lens 39b, to convert the image into a collimated image, as best shown in FIG. 4. After the light impinges on the facets 32a of a rotating polygon mirror 32, the collimated beam is reflected towards a scanning surface 34. An anamorphic optical system comprising a first convex cylindrical lens 37 and a condensor lens 33 is disposed intermediate the rotating polygon mirror 32 and scanning surface 34 to convert the collimated image to a converging image. (col. 3, lns. 22-40)
U.S. Pat. No. 4,906,061 discloses scanning a surface with a laser light beam. The light beam is projected through a collimator lens 2 to a rotating mirror 3, the light beam is deflected by the mirror 3 and applied through a f.THETA. lens 4 to converge on the surface to be scanned. The rotating mirror 3, as shown in FIG. 1, may comprise a rotating polygon mirror or a pyramidal mirror. The collimator lens 2, as best shown in FIGS. 2A and 2B, is movable along the optical axis to correct the curvature of the field.
An image mover for a light projector has been desired where the size of the steering mirror, rotator assembly and their associated parts and motors are reduced. This size reduction of the steering mirror and rotator assembly allows higher acceleration and velocity movement of the image with smaller motors.